Integrated circuits (ICs) are subject to a variety of failure modes due to improper manufacturing. Some of these failures occur only when the IC is operated at high temperature. Some failures occur only after the IC has been operated for some period of time which is substantially less than the predicted lifetime of the device. These latter failures are called "infant failures". Because operating the IC at high temperature for a short period of time accelerates infant failures, such condition may be used to screen for infant failures so they may be identified and discarded before the IC is deployed in actual use in a system.
To detect high-temperature failures, ICs are individually tested in special temperature chambers which raise each IC to the prescribed temperature. However, some ICs do not exhibit temperature operational problems until they are put into systems. It is often impractical to control the temperature of the IC in a system environment to see if it is defective at high temperature. It would be advantageous to be able to control its temperature under external command and without the need to place it in a special temperature controlled chamber.
Infant failures are commonly screened by a process called "burn-in". In this process, many ICs are loaded onto special burn-in boards which are placed into special temperature regulated burn-in ovens. They are then operated at a predetermined temperature for a period of time, which is often one week or more. In some cases they are life-tested, that is, they are subject to burn-in for 1000 hours or more. Burn-in and life-testing are expensive processes because of the equipment cost and because of the time the equipment is required to be dedicated to a relatively small number of ICs.
Temperature sensing and control means are not uncommon in ICs. Many methods are known to sense the temperature of an IC and generate a control signal. However, none of these circuits have been employed for reliability or burn-in purposes. Internal heating and regulating the temperature of an IC for high temperature or reliability testing is a novel idea. For example, in U.S. Pat. No. 4,165,642 entitled "MONOLITHIC CMOS DIGITAL TEMPERATURE MEASUREMENT CIRCUIT", by Robert J. Lipp, the temperature is sensed by measuring the voltage across a base-emitter junction and comparing that to a reference voltage generated by a band gap reference circuit. A digital control output is generated. Nothing is mentioned regarding heating and temperature sensing for burn-in or reliability testing. U.S. Pat. No. 4,497,998 entitled "TEMPERATURE STABILIZED STOP-RESTART OSCILLATOR" by Burnell G. West, has heating, sensing and controlling means for regulating the temperature of an IC. This apparatus is used to control the temperature for stabilizing an oscillator.